The historical and classical mining province of
Bergslagen in Sweden remains a potential exploration target. New metallogenetic
interpretations, 3D/4D geological modeling, performance of advanced
multidisciplinary methodologies and innovative technology applications may
generate further challenging opportunities in terms of locating deeper seated ore
bodies and unlock feasible critical raw materials associations. A major
mineralised belt is the one defined, from north to south, by the well known
mines and occurrences in Stråssa, Håkansboda, Lovisa, Stripa, Guldsmedshyttan,
Fanthyttan and Leja. A regional scale N20-40oS striking shear zone,
imposed upon a lithostratigraphic sequence of acidic metavolcanic rocks
interbedded with horizons of crystalline carbonates, seems to be the main
structure controlling the spatial extension, and most probably the oxide and
sulfide ore forming mechanism in the area.
Shear-related ductile and brittle deformation appears more likely to be
the reason for the origin of the banding, folding and fracturing observed. Up
to now the genetic origin of the mineralizing processes and ore forming systems
were referred to either sedimentary exhalative (SEDEX), mainly due to the
occurrence of Banded Iron Formations (BIF), and/or to carbonate replacement skarn-related
deposition.
Major questions and issues to be highlighted
and addressed, particularly as part of the recently started EU-funded X-MINE
project, are:
·
The
presence of SEDEX mineralisations and they relate timely to ore formation
·
The
role of shear-zone deformation in controlling mineralizing fluids and ore
deposition in relation to the metavolcanic and interbedded marble contact zones
·
The
role of carbonate/marble beds in the formation of skarn/manto-style deposits
·
The
role of crosscutting fault systems and their intersections with shear zone and carbonate
rocks in forming ore concentrations
·
The
identification and characterisation of alteration processes in relation to
mineralisations, based on both mineralogy and lithogeochemistry
·
A
better understanding of why various types of mineralisations, in terms of
mineralogical and geochemical composition, are formed and found in different
locations and parts within a pretty similar setting of bedrock lithologies, though
strikingly controlled alongside the shear-zone structure and carbonate rocks
lithostratigraphy, such as,
o
Iron
ore in Stråssa
o
Cu,
Co, As, Sb, Au, Bi in Håkansboda
o
Zn,
Pb in Lovisa
o
Iron
ore in Stripa
o
Ag,
Pb in Guldsmedshyttan
o
Cu,…
in Leja
·
How
is this part of the belt, ore geologically connected and linked to its
northward extension towards Bastnäs and Norberg, where also a potential REE
component is added to the mineral system, to form the so called REE-line
·
Finally
which is the role of the granitic, but also the metamafic intrusions in
sourcing heat, mobilizing hydrothermal fluids and providing metals
